Billionaire Bill Ackman is growing increasingly optimistic. After warning “hell is coming” back in March, the highly-respected stock picker has started singing a different tune, arguing that the possibility of hydroxychloroquine and antibiotic treatments, the ramping up of antibody tests, government stimulus and low interest rates are encouraging signs.It’s no wonder market watchers track Ackman’s moves religiously. The CEO of investment firm Pershing Square Capital Management was able to take $27 million and turn it into $2.6 billion using a series of credit-default swaps just last February. How does he do it? Before Ackman even thinks about pulling the trigger on an investment, he relies on a comprehensive three-pronged strategy to determine the strength of the opportunity.“The most important thing for us is that the business quality is extremely high. It's got to be what we call a simple, predictable free cash flow generative business,” Ackman explained. The approach also involves taking a long-term holistic view of a stock as well as comparing the price to the intrinsic value, with his methodology resembling that of fellow investing guru Warren Buffet.Looking to Ackman for inspiration, we ran two stocks the hedge fund manager snapped up recently through TipRanks’ database to get the analyst community’s take on them. It turns out that the billionaire isn’t the only bull as each name is Buy-rated.Restaurant Brands International (QSR)The name Restaurant Brands International might not ring any bells, but the names of its restaurant chains, which include the likes of Burger King, Popeyes and Tim Hortons, definitely will. After gaining an additional vote of confidence from Ackman, the stock has made its way onto the Street’s radar.In a May 4 filing, Pershing Square disclosed that it added even more shares to its QSR holding, 9,086,895 to be exact, with a spokesperson for the firm calling the name “undervalued” and “an attractive investment.” This purchase increased its position by 45.5%, and as a result, the firm now owns 9.6% of the company.QSR also counts several Wall Street analysts as fans. Oppenheimer’s Brian Bittner is among those singing the company’s praises. The five-star analyst calls QSR his “top large-cap pick”, with it boasting one of the best risk/reward profiles in his coverage universe.Expounding on this, Bittner stated, “QSR currently represents our top large-cap pick. An analysis of updated 2021 estimates across peers suggests QSR now trades at a 27% discount despite having the lowest earnings risk vs. consensus, in our view. And while its above-average growth algorithm remains overlooked, its Popeyes brand is becoming particularly underappreciated as the business could soon pass Tim Horton's in size with explosive runway for further upside.”Looking at its Popeyes segment, Bittner points out that the chain is already returning to pre-COVID-19 levels, or 20-30%-plus. In addition, while comps were flat in the last two weeks of March, its competitors were down 30%-plus. The analyst argues that it’s also very possible that Wall Street’s estimates for sales will get a lift.When it comes to the Tim Hortons brand, Bittner acknowledges that investors have been concerned about this aspect of the business. However, the analyst isn’t surprised by the recent weakness as COVID-19 has altered morning routines, and like other coffee chains, a rebound is expected in 2021. This prompted him to comment, “We believe investor worries around Tim Hortons issues do not justify the current disconnect in shares and we recommend taking advantage.”As Burger King is also showing signs of an improvement, the deal is sealed for Bittner. The analyst kept both an Outperform rating (i.e. Buy) and $60 price target on the stock, implying 23% upside potential from current levels. (To watch Bittner’s track record, click here)In general, the rest of the Street agrees with Bittner. With 15 Buys and 3 Holds, the word on the Street is that QSR is a Strong Buy. At $59.47, the average price target brings the upside potential to 21%. (See QSR stock analysis on TipRanks)Howard Hughes Corporation (HHC)With over 80,880 acres of land, Howard Hughes develops master planned communities where it owns and operates mixed-use, office, retail, multi-family and hospitality properties. While Ackman doesn’t dispute the fact that the company has “significant short-term exposure” to the COVID-19 pandemic, he thinks the current valuation presents an exciting opportunity.To this end, Pershing Square boosted its HHC holding, which previously came in at 6,384,239 shares, by a whopping 156.7%. Disclosing the buy on March 31, the firm went in on 10,002,596 shares, giving it a 29.8% stake.BWS Financial analyst Vahid Khorsand also has high hopes for the company. The driver of his bullish thesis? Khorsand cites the company's March 27 capital raise, which included a share offering of 12 million shares and ultimately raised $582 million. It should be noted that it was during this offering that Ackman’s firm purchased the shares.Like other players in the industry, HHC has faced COVID-19-induced headwinds related to generating revenue from its hospitality assets, selling land and collecting rent, but Khorsand argues that this capital frees up the balance sheet and acts as a “capital cushion that could allow it to absorb a decline in revenue while completing projects in development.”Even though development activity will be limited to projects underway with deposits in hand or near completion, Khorsand said, “With the capital raise out of the way, HHC can focus on managing the income statement for the remainder of 2020.” The analyst added, “In the meantime, HHC has the capital liquidity to operate as a going concern with an asset portfolio we believe could help bolster HHC’s cash position once the economy begins to normalize.”There’s a risk that the lockdowns or stay-at-home orders could be extended, but Khorsand remains optimistic. As a result, he reiterated a Buy rating. He did however cut the price target from $150 to $80, but this still leaves room for shares to climb 54% higher in the next year. (To watch Khorsand’s track record, click here)Judging by the consensus breakdown, it has been relatively quiet when it comes to other analyst activity. Only one other review was published recently, a Hold, making the consensus rating a Moderate Buy. Additionally, the $70 average price target implies shares could surge 35% in the next twelve months. (See Howard Hughes stock analysis on TipRanks)To find good ideas for stocks trading at attractive valuations, visit TipRanks’ Best Stocks to Buy, a newly launched tool that unites all of TipRanks’ equity insights.